1. Field of the Invention
The present invention relates to angioplasty procedures, and more particularly to a device and method to prevent arterial plaque from being dislodged from the arterial wall in procedures such as, for example, percutaneous transluminal coronary angioplasty (PTCA) or percutaneous transluminal angioplasty (PTA), especially carotid PTA, and migrating into the patient""s vasculature.
In typical carotid PTA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the common carotid artery. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient""s carotid vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent is crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient""s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter. The stent also may be of the self-expanding type.
A danger always present during any intravascular procedure is the potential for particles of the atherosclerotic plaque, which can be extremely friable, breaking away from the arterial wall. These emboli can subsequently migrate through the patient""s vasculature to sensitive organs such as the brain, where they may induce trauma.
2. Description of the Prior Art
The majority of devices that have been proposed to prevent the problem of emboli generated during an angioplasty procedure fall into either of two broad categories: devices that simply intercept emboli flowing within the patient""s blood stream, and devices that intercept as well as remove such emboli from within the patient""s body. A device typical of the first category is described by Goldberg in U.S. Pat. No. 5,152,777 and consists of a filter comprised of a plurality of resilient, stainless steel wire arms joined at one end so as to form a conical surface, and having rounded tips at their other ends to prevent damage to the vessel walls. Alternatively, the filter may be attached to a catheter through which lysing agents can be introduced to dissolve any trapped emboli. Most devices of this type are intended for permanent deployment within the patient""s body, and thus pose the risk of trapping sufficient emboli to adversely affect the flow of blood within the vessel in which they are deployed. Furthermore, any foreign object in the body tends to provoke a response from the immune system and over time can lead to endothelial cell formation.
Devices that remove emboli from the blood stream are similar to the filter devices described above and are typically connected to a deployment device such as a catheter that permits their withdrawal from the vasculature. U.S. Pat. No. 4,969,891 to Gewertz, for example, discloses a removable vascular filter permanently attached to a wire sufficiently long to extend out of the patient when the filter is deployed within. The filter is comprised of a bundle of wires secured together and having end portions that flare outwards to form the actual filter element. The filter is introduced through a catheter and the filter wires expand on their own once released from the catheter to obstruct the vessel and strain the blood flowing therethrough. This device, and others like it, are not adapted for permanent deployment within the body and can only be used for limited periods of time, limiting their efficacy.
In light of the above, it becomes apparent that there remains a need for a device or method that will prevent friable plaque from breaking away from arterial walls during intravascular procedures and forming emboli in the bloodstream, that is easy and safe to deploy, and that may be easily removed or alternatively employed over extended periods of time with minimal adverse impact or immunological response.
The present invention addresses the above mentioned need by providing a sheath at the distal tip of a catheter to be expanded against an arterial wall and trap plaque therebetween. A stent or other intravascular graft subsequently can be partially deployed distally of the plaque, the sheath then can be removed, and the stent fully expanded to trap the arterial plaque and any emboli between the stent and the arterial wall.
Thus, in one aspect, it is an object of the present invention to provide a device for trapping plaque against a vascular wall comprising an expandable sheath mounted to the distal end of an elongated tube such as a catheter, the sheath to be expanded by a balloon against a mass of atherosclerotic plaque site lining the intima of a body vessel. In another aspect of the present invention, the expandable sheath is reinforced by an expandable element embedded within it.
In yet another aspect of the present invention, an assembly is provided for trapping plaque against a vascular wall comprising an expandable sheath mounted to the distal end of an elongated tube such as a perfusion catheter, a delivery catheter axially slidably disposed within the perfusion catheter, a self-expanding intravascular device such as a stent disposed within the distal tip of the delivery catheter, and a pusher rod axially slidably disposed within the delivery catheter.
It is a further object of the present invention to provide a method for trapping plaque against a vascular wall comprising the steps of expanding a sheath mounted to the distal end of an elongated tube such as a perfusion catheter against the plaque, inserting within the perfusion catheter a delivery catheter with a self-expanding intravascular device such as a stent or intravascular graft disposed within its distal end and a pusher rod disposed adjacent the intravascular device, positioning the delivery catheter distal tip within the expanded sheath, partially withdrawing the delivery catheter to allow the distal portion of the intravascular device to expand against the vessel wall at a location distal of the plaque, withdrawing the expanded sheath, and withdrawing the delivery catheter to expose the rest of the intravascular device and thus allow it to fully expand and trap the plaque against the vessel wall.